The present invention relates to turbine power plants and more particularly to large, stationary turbine power generators of the type used for utility services.
A typical stationary turbine power plant, known as Model Series 7001 simple cycle, single shaft, heavy duty gas turbine (Frame-7 machine), is available from General Electric of Schenectady, N.Y. In this and similar gas turbines, a seal is located between an axial compressor rotor and a stationary inner barrel member, a chamber within the inner barrel member being supplied with cooling air from the last stage of the compressor by a controlled amount of leakage through the seal. The cooling air is then utilized for cooling of a first turbine stage of the machine. A set of rotor bearings is located in the cavity.
Leakage in excess of a predetermined amount that is required for cooling of the turbine becomes parasitic and contributes to inefficiency of the machine. This is a serious problem in turbine power plants of the prior art, in that the labyrinth seals degrade in operation because of thermal expansions and other factors that cause knife-edge members and adjacent rotating elements of the seals to be worn away quickly, particularly during shut-down sequences. This is caused, for example, by shrinkage of the inner barrel member being more rapid than shrinkage of the rotor at the seal due to the rotor being more massive. Thus in the frame-7 machines, the bypass air flow increases to approximately 100,000 lb/hr from the 30,000 lb/hr that is considered optimal. Consequently, there is a loss of power that is believed to be between 1.5 MW and 3.0 MW.
Brush seals for gas-turbine engines are known, being disclosed, for example in “Brush Seals,” Directions, September 1993. As disclosed therein, a brush seal consists of densely packed metallic bristles that are welded between a down-stream backing plate and an up-stream side plate. In a typical round seal for aircraft turbine applications, the plates are ring-shaped, the bristles extending radially inwardly at a trailing lay angle and making an interference contact with a rotor element, so that the bristles become curved and follow the rotor as it grows and shrinks during engine operation.
Brush seals have not been applied to existing large power plant turbines for a number of reasons. For example, the existing rotor components, being made from elements of low carbon steel alloys that are selected for certain thermal expansion properties, are believed to be unsuitable as wear surfaces for contact by the bristles, particularly during the extended operation cycles that are demanded of stationary power plants. Suitable hardening of applicable compressor rotor members is believed to be prohibitively expensive, particularly in existing equipment.
Thus there is a need for an improved rotor seal for large stationary plants, that overcomes the disadvantages of the prior art.